DIgSILENT PowerFactory Application Guide
Distance Protection Tutorial DIgSILENT Technical DIgSILENT Technical Documentation
DIgSILENT GmbH Heinrich-Hertz-Str. 9 72810 - Gomaringen Germany T: +49 7072 9168 00 F: +49 7072 9168 88 http://www.digsilent.de
[email protected] r1049
Copyright ©2013, DIgSILENT GmbH. Copyright of this document belongs to DIgSILENT GmbH. No part of this document may be reproduced, reproduced, copied, or transmitte transmitted d in any form, by any means electronic or mechanical, without the prior written permission of DIgSILENT GmbH. Distance Protection Tutorial (DIgSILENT (DIgSILENT T Technical Documentation)
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DIgSILENT GmbH Heinrich-Hertz-Str. 9 72810 - Gomaringen Germany T: +49 7072 9168 00 F: +49 7072 9168 88 http://www.digsilent.de
[email protected] r1049
Copyright ©2013, DIgSILENT GmbH. Copyright of this document belongs to DIgSILENT GmbH. No part of this document may be reproduced, reproduced, copied, or transmitte transmitted d in any form, by any means electronic or mechanical, without the prior written permission of DIgSILENT GmbH. Distance Protection Tutorial (DIgSILENT (DIgSILENT T Technical Documentation)
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Contents
Contents 1 Introd Introduct uction ion
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2 Dis Distan tance ce Rel Relay ay Modeli Modeling ng
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3 Settin Setting g the the Dista Distance nce Rel Relay ay
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4 Cre Creati ating ng and and Edit Editing ing a Path Path
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5 Adding Adding More Rel Relays ays
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6 Cre Creati ating ng a New New Path Path
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7 Cre Creati ating ng a Time Time-Di -Dista stance nce Plot Plot
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8 Cre Creati ating ng a Block Blocking ing Sche Scheme me
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9 Mutual Compensation Compensation Factor Factor and Implementati Implementation on
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Distance Relay Modeling
Introduction
This tutorial demonstrates the modeling and editing of protective devices typically found in transmission networks. For most of the tutorial, the network that is used can be found, as an application example, in the 1987 edition of Protective Relays Application Guide (PRAG) published by GEC Measurements, paragraph 11.32. Some differences from the original example in the text have been introduced to demonstrate specific PowerFactory applications, as well as to model a more realistic example. Only for the “Mutual Compensation Factor and Implementation” chapter, a different network is used. As it is assumed that the user is familiar with basic editing of data, the network has been prepared for use, only requiring the editing of protection devices. Instructions to perform load flows and the observations of the results are thus left to the students discretion. It is also assumed that the student has completed the overcurrent protection tutorial so that the basics of relay modeling are familiar.
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Distance Relay Modeling
The textbook example uses a ’Quadramho’ relay. In this tutorial however, a ’Micromho’ relay will be used, which is very similar. The Micromho type characteristics are available in the tutorial project library. The steps we follow to model the relay are as follows: Note: Activate the “Distance Protection Tut 0” project.
• Right click on the cubicle feeding Line G from Station P. Select New Devices / Relay Model . . . as is shown below.
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Distance Relay Modeling
• A relay element data input window opens, where the new relay is named “Relay G”. • We select the relay type using the select button and look for the relay type in the project library. The project library should open with the relay type filter activated.
• There is only one distance relay type saved in the library, this has been placed there for use in this tutorial and of course this relay type is the Micromho that we want to use in this example. • We select this Micromho relay by double clicking on the relay type icon. The relay element data input window is now updated as shown below.
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Distance Relay Modeling
• Select Create CT to model a CT input to the relay. The CT data input window as shown below, opens.
• The CT element can be given a special name such as “CT G”, but this is not absolutely necessary. • Again we need to select a CT type from the project library. This is done by pressing selecting a type from the project library once again. Then select the “600/1 CT Type” from the project library. • The CT element data window is updated to show a 600/1 ratio. Of course, had the CT type been a multi-ratio CT, we would also need to select the CT ratio.
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Distance Relay Modeling
• The Location is not specified and therefore the CT is automatically modeled in the same cubicle as the relay. A specific location, other than the local cubicle, would only be used if current measurement was required from a different feeder that that in which the relay is located. • Press OK and the CT element is correctly modeled and visible in the relay element model. • Now a VT element must be created. To do this, the Create VT button is pressed. A element data input window, as shown below, opens.
• The VT is given a name “VT G”. • Note that the VT is defined in terms of a Type and Secondary Type . In other words the VT model consists of a separate primary and secondary. Firstly the primary type is defined by selecting the relevant type using the selection button. A drop down menu appears and we select the VT that is available in the project library. • Now the Secondary Type is selected from the project library using hte normal type selection procedure, this time for the Type in the Secondary section. Use the “Voltage Transformer Secondary” that is available in the project library. • Press OK and we are back to the relay element input window, but this time with a VT modeled in the relay. • Just as with real systems, we need to be sure that the relay model type is correct for the application. Double click on the Measurement element in the relay, and we notice that the relay has been rated with a nominal current of 1 A and a nominal voltage 110 V. These values correctly match the CT and VT input values. Pressing OK closes the measurement element. The Relay G has been modeled in place, but has not yet been set. This is our next step.
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Setting the Distance Relay
Setting the Distance Relay
The relay elements are set individually using the same settings proposed in the textbook, as follows: • Double click on the polarizing element. The window shown below opens.
• Note that the line k0 (described as kn, residual compensation factor adjustment in the ref. book) value is automatically calculated and displayed. As should be expected, the value of 0.49 at an angle of 7.8 degrees matches the textbook exactly. By pressing Assume k0 , the k0 setting is changed to 0.48, which is the closest available setting to 0.4893 for this relay. Press OK. • Double clicking the starting element opens the next setting window:
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Setting the Distance Relay
• The starting element consists of earth fault and over-current elements. It is important that these elements are set sensitively enough to pick up for all faults at the end of the setting zones. To determine this sensitivity we can use PowerFactory to calculate the 3-phase and earth fault currents at the end of zone 3 for relay on Line G. Using a fault impedance of, say, 10 Ohms, we give us a conservative value for setting the starting elements. For this tutorial the busbar at ’Substation R/B1’ at the end of Line J is faulted, using the complete calculation method. Respective resultant fault currents of 600 A and 410 A for 3-phaseand earth fault through Line G are calculated. • Set the Current, 3∗I0 to 0.6 sec.A and Current I>> to 1 sec.A. Press OK. • Double click on the earth fault measuring element for phase 1 called “PGZ1”. The window shown next opens.
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Setting the Distance Relay
• The secondary ohm impedance values of the first line are automatically calculated and shown. Assuming we want to set this element to 80% of the impedance of Line G, we calculate a value of 8.78 sec.Ohms (10.981 x 80%). Set the Replica Impedance to 8.78 and the Relay Angle to 65 deg. The branch angle reach is automatically calculated as 79.93% of the line impedance, confirming that the setting is correct. Press OK. • The Zone 2 reach must be set to cover the protected line plus 50% of the shortest adjacent line or 120% of the protected line whichever is the greater. For the application under consideration Zone 2 is set to cover the protected line plus 50% of the shortest adjacent line. Using the same procedure as for setting PGZ1, we set PGZ2 Replica Impedance to 15.37 sec ohm and the Relay Angle to 65 deg. • Again we set PGZ3 using the same procedure as for PGZ1 and PGZ2. This time we set the PGZ3 Replica Impedance to 65.89 sec ohm and Relay Angle to 65 deg. The Character Angle is kept at 90 deg (to maintain a circular tripping characteristic) and the Offset Impedance is set to 2.2 sec ohm. • The phase elements of PPZ1, PPZ2 and PPZ3 are all respectively set to be exactly the same as the earth fault elements of PGZ1, PGZ2 and PGZ3. • Double clicking on the Z2GD element (earth fault timer), opens the following window:
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Setting the Distance Relay
• Select time Z2GD Time Setting to 0.3 s. Press OK. • Repeat this procedure for Z3GD, setting the Time Setting to 0.6 s. • The same procedure is used to set Z2PD and Z3PD timers to 0.3 s and 0.6 s respectively. • The last element to be set is the logic element. In most cases, such as this one, it needs no setting. However, should we wish to trip a different breaker to the one in the same cubicle as the relay, we would need to define this here. For this exercise, we will not set the logic unit.
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Creating and Editing a Path
Creating and Editing a Path
When there are several relays in a system and one would like to check the settings of some of these distance relays, in series, it is beneficial to define a path. We define a path as follows: • Multi-select the busbars and lines from Station P Busbar B3 (132 kV) to Station R Busbar B1 by clicking on each of the elements along this path, while holding down the Control key. • Right click anywhere on this multi-selection. A drop down menu appears. Select Path. . . / New... as shown.
The following input window appears:
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Creating and Editing a Path
• The path to be created can be given a unique name for identification. Press OK. • The path selected should appear in red on the single line diagram. • Right click anywhere on the path and select Path. . . / Create R-X Plot on the drop down menu as shown next.
An RX Plot appears showing the settings of Relay G, as well as some line impedances. Note that the earth fault and phase fault impedance elements are on top of each other for each zone. This can be seen by double clicking on, say, the outer zone setting (Zone 3). The following window appears:
• Relay elements can be set directly from the RX plot by double clicking on the displayed characteristic. In case of there being more than one plot being on top of another, as we have here, a window will open in which we must then select the relevant relay setting to be edited. • After selecting the element to be set or changed, press the Edit Object tool on the toolbar, and the setting sheet of the selected element appears. Alternatively, double click on the element icon to arrive at the setting sheet.
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Creating and Editing a Path
• Double click anywhere on the diagram (but not on a plot) and the relay plot editor appears. Select Options and the window shown below appears.
• Select “Ph-Ph & 3-Ph” in the Relay Units options. Press OK and OK again to return to the graphic. • Now only the Phase-Phase and 3-Phase Distance elements are shown on the RX Plot. The vertical lines represent the impedance of the power transformers.
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Adding More Relays
Adding More Relays
The aim of any protection engineer is to ensure that coordination between different distance and overcurrent relays is correct. This coordination can be checked using RX plots, TimeDistance plots and time Overcurrent plots. Defining paths for the relays to be coordinated is a tool that may be used in order to make maximum use of these different plots. Before this can be demonstrated, more relays must be added to our project. In the next few steps, we add an overcurrent relay to the source side (Station Q side) of Line K, and a distance relay at the source side of Line J, as follows: Note: Activate the “Distance Protection Tut 1” project.
• Right click on the Substation Q cubicle connected to Line K. Select New Devices. . . / Relay Model . • Name the relay “Line K OC”. • Select the “Standard OC Relay” type relay from the library. • Select Create CT. From the library select the type to be a 400/200/1 CT and press OK. • Note that the CT defaults to the lowest available ratio of 200/1. We want to use the 400/1 ratio and must select it in the Primary Tap drop down menu. Press OK. • Set the three-phase over-current element to 5 p.u. and the time multiplier to 0.2 (double click on the Toc3Ph element field to access these setting fields). Press OK. • Right click on the Station Q cubicle connected to Line J. Select New Devices. . . / Relay Model . • Name the relay “Relay J”. • Select the “Micromho” type relay from the library. • Select Create CT. On the window that appears, select the Type arrow down. From the library select the 600/1 CT and press OK. • Select Create VT. Define both primary and secondary VT type as before for “Relay G”. • Set the relay as follows: PGZ1 = PPZ1 = 18 sec.Ohm; PGZ3 = PPZ3 = 60 sec.Ohm; Z3 Offset Impedance = 0;
PGZ2 = PPZ2 = 30 sec.Ohm; Relay Angle = 65 degrees; Characteristic Angle = 90 degrees
The new distance relay “Relay J” is already in the defined path. The relay can either be added to the existing RX plot, or a new RX plot could be generated containing all relays in the path. The second option is chosen: • Right click on the red path in the grid and select Path. . . / Create R-X Plot . • A new RX plot appears showing both “Relay G” and “Relay J” impedance plots.
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Creating a New Path
Creating a New Path
Say we need to check the tripping coordination between “Relay G” and “Line K OC” relays. One way to do this would be to use a time-distance plot. First a new path needs to be defined: • Multi-select the new path shown below holding down the control key. Make sure the Station Q 132 kV bussection cubicle/breaker is also selected in the path, or you will receive a warning “Path not complete”. To do this, you may need to enlarge the area around the bussection. • Select Path.. . / New.. . .
• A dialogue for the new path appears. Change the path colour to green to differentiate from the first path. Select OK. The new path will appear in green.
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Creating a Time-Distance Plot
Creating a Time-Distance Plot • Right click on the newly created green path and select Path. . . / Create Time-Distance Diagram . Make sure that you do not right click on a combined path, but select a part of the path that is unique to the green path in order to create the correct diagram.
• Two plots are shown, but these need to be further defined. Double click anywhere on the plots. The screen shown will appear.
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Creating a Time-Distance Plot
• Only a forward plot is required. In the drop down menu next to “Diagrams”, select Forward . • For the “Reference Relay, Forward” select “Relay G”. • Select the Short Circuit Sweep method option. • Press OK. • Update the plot by clicking on the “Rebuild” icon shown below.
• The curves may not appear immediately as the scale could be incorrect. Press the “Scale X-Axis Automatically” and “Scale Y-Axis Automatically” buttons on the second toolbar, and the curves should appear as shown next.
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Creating a Time-Distance Plot
From the diagram it is noticed that the distance relay (Relay G) will operate faster than the overcurrent relay. This would cause incorrect tripping. To set this right, take the following steps: • Double click on the green curve of the over-current relay. Change the “Current Setting” to 1.5 p.u. and “Time Dial” to 0.1. • Press OK. • Double click on the Zone 2 part of the red distance relay (Relay G). The PPZ2 window opens. Select Timer . The Z2PD window opens. Set the “Time Setting” to 0.5 seconds. Press OK and OK. • Double left click on the Zone 3 part of the red distance relay. The PPZ3 window opens. Select Timer. The Z3PD window opens. Set the “Time Setting” to 1.0 seconds. Press OK and OK. • Press the “Rebuild” button on the second toolbar. • After the recalculation has been completed, rescaling the Y-Axis may be required. This is done by pressing the “Scale Y-Axis Automatically” button on the second toolbar. • The Time-Distance diagram now appears as shown below.
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Creating a Time-Distance Plot
It is now clear that for three-phase faults without any fault impedance along the green path, tripping coordination will be correct.
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Creating a Blocking Scheme
Creating a Blocking Scheme
Distance protection usually involves teleprotection schemes in order to improve the protection degree offered by the distance relays. Several schemes have been developed, among which can be found: • Permissive Underreach Transfer Trip or PUTT • Permissive Overreach Transfer Trip or POTT • Blocking Scheme The reader can find more details about each of the mentioned teleprotection schemes above, consulting the specialized literature. For this tutorial, we will implement a blocking scheme, whose main characteristics are summarized below: • The scheme will use a blocking signal by means of a reverse zone detection. • The blocking signal will be sent to the relay of the opposite side of the transmission line. • If no blocking signal is received, and the relay detects a fault in zone 2, it will operate instantly. • If a blocking signal is received, then the fault is outside the transmission line and the relay will start the timer of zone 2. A model has been prepared for use in the library. It includes two slots, where two relays can be assigned for the blocking scheme. It must be only at one side of the transmission line, but has to refer to each distance relays at both sides. The procedure to include the blocking scheme is as follows: Note: Activate the “Distance Protection Tut 2” project.
• Go to the library folder and locate the Micromho relay model. Make a copy and name it as “Micromho wBlock”. • Right click on the new copied relay model and select “Show Graphic”. • Since the “Micromho” model relay has only six distance protection zones, three for Phase faults and three other for Residual faults, we will use the Zone 3 as reverse zone, to detect and block the external relay. Locate inside the connection diagram the “PPZ3” and “PGZ3” blocks. • Create a slot and enter the data as shown in the figure below.
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Creating a Blocking Scheme
• Connect a signal from the output of the “PPZ3” block to the first input of the “Logic OR” block. With the same procedure, connect the signal from the “PGZ3” block to the second input of the “Logic OR” block. • Connect a signal from the output of the “Logic OR” block to the output frame, as shown below.
• Now, the relay must discriminate if the fault is inside Zone 2 and check if the blocking signal Distance Protection Tutorial (DIgSILENT Technical Documentation)
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Creating a Blocking Scheme
has been received. Edit the “Logic” block and add three more input signals: y receive , Z2P and Z2G . • Use the same procedure as before to connect the outputs of the “PPZ2” and “PGZ2” blocks to the corresponding inputs (“Z2P” and “Z2G” as defined before) of the “Logic” block. • Connect a signal at the beginning of the frame to the input of the y receive signal in the “Logic” block, as shown below.
(a) Beginning of the signal
(b) End of the signal
Please note that, in general, the procedure to adapt the relay model for a teleprotection scheme will be the same. The difference relies on the location of each signal and the blocks to connect to in order to achieve the blocking scheme. Since we have made modifications to the internal structure of the relay, it must be updated. Also, we have to define the logic for the blocking scheme. The procedure is as follows: • Edit the Micromho wBlock relay and click on Slot Update . This will update all slot definitions and create any Types if they do not exist at the moment. Please ensure that the Slot quantity is 17 and the “Logic OR” is assigned to the relay. • Edit the “Logic OR” block. Set “Breaker Event” up to None and insert the input signals y send ph and y send gnd and the output signal y send . • Go to the “Logic” tab and insert the following code: y send=y send ph.or.y send gnd . Click OK. • Now edit the “Logic” block. Insert the input signals y receive , Z2P and Z2G and the output signals REVBLOCK and REMTRIP . • Set User Defined Settings to “only Logic”. • Go to the “Logic” tab. Insert the following code: REVBLOCK=NOTRIP REMTRIP = Z2P.or.Z2G.and..not.y receive.and.REVBLOCK
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Creating a Blocking Scheme
• Add at the end of the tripping signals, 94 1ABC and 94 2ABC , the value .not.REMTRIP . Now we will test the blocking scheme. First of all, we have to add some relays to our model. • Edit the devices inside the “Line G” cubicle and copy the “Relay G”, “CT G” and “VT G” elements. Click Close. • Edit the other cubicle and paste the elements. • Set the relay as follows: PGZ1 = PPZ1 = 8.78 sec.Ohm PGZ2 = PPZ2 = 15.37 sec.Ohm PGZ3 = PPZ3 = 7.91 sec.Ohm Relay Angle = 65 degrees Z3 Offset Impedance = 0 Characteristic Angle = 90 degrees PPZ3 and PGZ3 Tripping Direction = Reverse Z3PD and Z3GD Time Setting to the max. possible value . • Edit the Starting unit of the relay and set the Current, 3∗I0 to 0.2 sec.A and Current I>> to 0.2 sec.A. Press OK and OK. Now we have to add the blocking relay to whichever cubicle in the transmission line. • Copy the newly added relay and edit the opposite cubicle at “Substation P”. • Create a “New Object” and select “Relay Model”. • Assign the “Blocking Model” Relay Type from the Library to the new relay. • Paste the Relay object onto the Slot “Relay 2”. Click OK. • Copy the relay Relay G and paste it in the the Slot “Relay 1”. The relay should look as shown below
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Mutual Compensation Factor and Implementation
Now that everything has been set, is time to create a Time-Distance Diagram and see the operation of the blocking scheme. Follow the procedure described before to create a TimeDistance Diagram. After some scale adjustments and showing only the relays of “Line G”, the diagram should look like in the figure below.
As you can see, the operation of the relay for Zone 1 covers 100% of the line, meanwhile the Zone 2 will operate for faults beyond the “Line G” Transmission Line.
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Mutual Compensation Factor and Implementation
When a distance relay is protecting a transmission line, which goes through a parallel circuit at the same tower, a coupling effect will take place. Meanwhile a full transposition of the circuits can overcome most of the mutual impedances between phases, until they reach a very small or negligible value, the mutual zero sequence coupling will still be present. This is due to the fact that the I0 zero current components are in phase, and the zero sequence flux linking to the other transmission line in parallel will not add to zero. Due to this, the impedance measured by a distance relay under phase to earth fault conditions will not represent exactly the impedance to the fault point. It can be proven that the positive sequence impedance measured by a distance relay, under a single phase to ground fault at “m” in per unit of the line, will be as described in the equation below:
mZ 1L =
Va Ia
+ Z0L-Z1L 3I 0 + 3Z1L
Z0m 3I 0m 3Z1L
(1)
Equation ( 1) implies that two factors are needed to be known in order to have an accurate measure of the apparent impedance to the fault. The first factor in bold corresponds to the k0 factor, while the second is the k0m compensation factor. With the help of PowerFactory we can determine this factors, although one of them (k0) can be automatically calculated inside the relay model and only an update of the value is actually needed.
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Mutual Compensation Factor and Implementation
Note: Activate the “Distance Protection Tut 3” project.
To illustrate this scenario, a test model has been prepared for use. It includes two 220 kV busbars and two transmission lines coupled at the same tower, and an external grid is feeding a 100 MW load. We will be using a Siemens relay model, the 7SA513 internal version 14.1.7 for PowerFactory . The 7SA513 relay uses a special definition to compensate earth faults and mutual coupling effects. Instead of directly using the k0 and k0m values as per definition, it decouples the resistive and inductive components. The definition, as included in the Siemens relay manual, is as follows:
RE RL
X E X L
1 = 3
1 = 3
RM RL
X M X L
R0
·
X 0
·
1 = 3
1 = 3
R1
X 1
−
1
−
(2)
(3)
1
·
(4)
·
(5)
R0M R1
X 0M X 1
Since R 1 , X 1 , R 0 and X 0 can be obtained directly from the transmission line dialog, the factors corresponding to equations ( 2) and ( 3) can be calculated. The dialog can be accessed by editing any of the coupled lines. The factors of equations ( 6) and ( 7) for mutual compensation, need the R 0M and X 0M values in order to be properly calculated. To obtain this values, please follow the following procedure: • Edit any of the coupled lines by left-clicking on one of them and select “Edit Data. . . ”. • Click on the arrow pointing to the “Line Couplings” object. • Inside the “Geometry” field, double click on the “Tower Type” object. • Go to the “Load Flow” tab. Click on the black arrow at the upper right corner of the matrix arrangement and select the Electrical Parameters to be displayed as shown in the figure below.
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Mutual Compensation Factor and Implementation
• Look up for the mutual zero sequence Resistance and Inductance in the corresponding matrices. They are in the row 1, column 2 and row 2, column 1 position for both matrices. We can see that the value for the R0M is 0.1408 Ohm/km and for X 0M is 0.9243 Ohm/km. • Note that another option to display the R0M and X 0M values would be to click on the “Calculate” button. This will display the matrices in the Output Window of PowerFactory . Now we can determine the values of
RM RL
X M X L
RM RL
1 = 3
1 = 3
and
XM XL
, as shown below.
·
0 1408
= 1 .2383 [−]
(6)
·
0 9243
= 0.6944 [−]
(7)
.
0.0379
.
0.4437
These values must be entered in the polarization block of our next new relay model. However, since we need the current value from the adjacent line, is easier to first define a CT in the corresponding cubicle. To do this follow this procedure: • Right click on the adjacent cubicle where the relay is not going to be inserted and select “Edit Devices” • Add a new “Current Transformer” and use the 600/1 Type. • Click OK and Close. Now that we have defined the “Mutual CT”, is time to create our new relay. • Follow the procedure as stated in previous chapters to define a relay model. Use the 7SA513 1A model. • Define a CT of 600/1 A and a VT of 220000/110 V for the relay. • Define the “Ct-Mutual” slot to be referenced to the CT of the adjacent line. Distance Protection Tutorial (DIgSILENT Technical Documentation)
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Mutual Compensation Factor and Implementation
• Check if the secondary values of the measurement blocks are properly defined according to the CT and VT values. • Edit the “Polarizing” block. Ensure that the values entered are as in the figure below.
Please note that clicking on the “Assume Re/Rl” and “Assume Xe/Xl” buttons, the corresponding values for the “Earth Factor” are automatically updated. However, the values for the “Mutual Earth Factor” must be entered manually. • Edit the starting block. Since it is starting from an “Impedance Z” type, we have to define the area from which is going to detect a fault condition. For our purpose we will define the widest area possible. Go to the “Impedance” tab and insert the values as shown in the figure below.
• Set the relay as follows:
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Zone Z1 Z2 Z3
+X Reach 31.95 sec.Ohm 47.92 sec.Ohm 100 sec.Ohm
+R Resistance 63.9 sec.Ohm 63.9 sec.Ohm 63.9 sec.Ohm
+R Resistance (PH-E) 63.9 sec.Ohm 63.9 sec.Ohm 63.9 sec.Ohm
Table 9.1: 7SA513 Relay parameters • Set the time zones as shown in table 9.2: Timer ZT1 ZT2 ZT3 ZT4 T5
Value 0s 0.40 s 0.80 s 10.00 s Out of Service
Table 9.2: 7SA513 Relay parameters
Now that the relay has been set, we will create a RX plot and check if the mutual compensation is working correctly. • Create a RX plot of the newly added relay. • Go to the “Options” menu of the RX Plot. • Define to be displayed only the Ph-E zones in the “Relay Units” field. • Uncheck the box corresponding to the “Starting” zone. • Go to the “Legend” tab and check the box to display the “Tripped Zones”. Click OK. • Edit the RX Plot. Change the “x-Min.” and “y-Min.” values to -7 and -4 respectively. • Set “Auto scale” to On . Click OK. Now perform a “Single Phase to Ground” fault at 75% of the line where the relay is. Use the IEC 60909 Method. Click on Execute and go to the created RX Plot. You should see something as in the figure below.
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